Humans aren't the only ones who hunt with weapons -- a troop of chimps in the wild have been observed crafting sharp spears to stab their prey.

The technique, described in the latest issue of the journal Royal Society Open Science, could have originated with the common ancestor of humans and chimps, suggesting that the earliest humans hunted in a similar manner.

"The tools (spears) are made from living tree branches that are detached and then modified by removing all the side branches and leaves, as well as the flimsy terminal end of the branch," lead author Jill Pruetz told Discovery News.

"Some individuals further trim the tip of the tool with their teeth," added Pruetz, who is a professor in the Department of Anthropology at Iowa State University. "They average about 75 centimeters (around 30 inches) in length."

Pruetz and her team watched chimpanzees from a site called Fongoli in southeastern Senegal, West Africa, making spears in this manner.

Spear in hand, the chimps would sneak up on bushbabies -- small, big-eyed primates -- and stab them to death. Bushbabies, which are nocturnal and are also called "galagos," spend much of their days snoozing in tree cavities. They can become an easy filling meal for a spear-wielding chimp.

The researchers noted that female adult chimps made and used spears more often than adult males. The males relied more on their size and strength for hunting. Female chimps are almost always hindered by infants that ride on their backs or bellies, so spear hunting is far more effective for them than attempting to chase down prey.

The researchers suspect that a female primate invented the world's first spear.

"In a number of primate species, females are the innovators and more frequent tool users, so I think it is possible that a female invented this technique," Pruetz said.

Dominant males at Fongoli support females and younger males by allowing them to keep their own kills, she added. This is rare, as in most chimp troops, large males steal prey from subordinates.

The Fongoli chimps are the only known non-human primates that systematically hunt large prey with weapons, so the site itself is of interest to the researchers. It is a savanna with a dry season that lasts over seven months. Early humans might have faced comparable conditions that led to greater reliance on meat consumption and efficient hunting methods.

"Vertebrate prey are less readily available to chimpanzees in Fongoli than they are at other, more forested sites, so the Fongoli chimpanzees got inventive and came up with a way -- that is, a weapon -- to ensure greater hunting success," he explained, adding that bushbabies bite when attacked, so the spear creates a safe distance between the hunter and the bushbaby's teeth.

While human hunting might have had humble beginnings involving stabbing small prey, Pickering thinks that early human males quickly took this to a whole other level by hunting in coordinated groups.

"Hunting large animals in groups is advantageous because of increased vigilance -- more eyes -- and the potential to recruit others for defense if one hunter gets into trouble," he said.

"Moreover, there's no getting around the fact that most males are bigger and stronger than are most females, and thrusting or throwing a spear into a big, thick-skinned antelope or zebra is going to require more power than stabbing a galago."

Animal tool use is far more common than previously thought, with fish recently added to the animal tool wielder's list. Here, a green wrasse picks up a clam. The fish later uses a rock as an anvil to smash open the clam.
Such underwater cleverness should come as no surprise, according to Culum Brown, director of advanced biology at Macquarie University. "Fish are always ignored when it comes to cognition," he told Discovery News. "That is largely due to our self-centered view of evolution. But even ignoring that bias, we would still seldom study fish because they are simply hard to observe."
Added Brown, whose findings are outlined in the latest issue of the journal Fish and Fisheries, "I'm sure tool use is far more common in fish than we realize."

Fish aren't the only underwater tool users. Dolphins break off sponges and wear them, but it's likely not a fashion statement.
"We believe that the marine sponge acts as a kind of glove to protective their sensitive rostra," marine biologist Michael Krützen of the University of Zurich told Discovery News.
"That probing (of the sea floor) might disturb fish that hide in the sand, which would then be easy targets for the dolphins."

Brown believes that "many animals resort to tool use when they lack the physical capability to access a resource, nearly always food, without the specific aid of a tool."
This photo shows a selection of sticks altered by chimpanzees at Kibale Forest National Park in Uganda to get at honey and other food.

Animals may use tools for defense, as does this decorator (also sometimes called "dresser") crab.
The crab possesses Velcro-like hooks on its shell that hold "accessories," which in this case are living coral polyps and sea anemones.
The other creatures give the crab a bottom-of-the-sea look that helps to disguise it on the reefs where it lives.

The closer animals are to our own species, the more their tool usage seems human-like.
This adult female gorilla named Leah from Nouabalé-Ndoki National Park in northern Congo, turned a big branch into a multi-purpose tool.
She used it as a walking stick, for postural support, and to test both the substrate and the water depth. Leah proves three aspects of animal tool usage highlighted by Brown.
"First, the animal has to be in an environment where suitable tools are available," he said. "Second, the animal has to have the physical and mental capacity to use the tool. Third, the physics of the environment make tool-use possible."
For the latter, he points out that fish don't have hammers because swinging them underwater "is really hard work and not very effective."

Tools don't always provide the fastest, easiest solution to problems.
In the case of New Caledonian crows, for example, their use of sticks to dislodge wood-boring beetle grubs from rotting tree trunks requires a lot of time and practice. Why do crows even bother with the sticks then?
Christian Rutz of the University of Oxford and colleagues investigated the benefits of this tool use by analyzing how different types of food contribute to individual crow diets.
As it turns out, just a few beetle larvae pulled out by sticks can satisfy a crow's daily energy requirements. So all of the extra effort is worth it.

Sometimes tools can aid in sudden life or death matters.
This small octopus from East Timor was seen on a night dive hiding between a nutshell and a clamshell.
When things got quiet, the octopus snuck out, carrying the shells. Sensing threats, it then clamped itself back between the portable hideout.

One of the most unusual animal tools is a "kiss squeak toy" that orangutans construct out of leaves.
Madeleine Hardus of the Behavioral Biology Group at the University of Utrecht told Discovery News that the resulting noise is hardly a love call. Instead, orangutans produce it when predators startle them, or they are otherwise disturbed.
"As far as I and my colleagues know, no other primate emits kiss squeak sounds," Hardus said.
"Male great apes can use their hands during the production of calls, such as buttress-drumming in chimpanzees, chest-beating in gorillas and snag-crashing in orangutans, but in these examples, calls are not modified; they're added with other acoustic elements. Only kiss squeaks are known to be modified."

It may not be pretty, but mammal dung serves as a useful tool for burrowing owls.
The owls collect the dung and spread it around the entrance to their homes, as seen here. Dung-consuming beetles find the bait irresistible. As the beetles are investigating the fragrant balls, the owl comes out for its crunchy bug dinner.

Our human ancestors were using stone tools and eating meat from large mammals nearly a million years earlier than previously thought, according to a Nature study that pushed back both of these human activities to around 3.4 million years ago.
The first known human ancestor tool-wielder and meat-lover was Australopithecus afarensis, according to the study. This species, whose most famous representative is the skeleton "Lucy," was slender, toothy and small-brained.
"By pushing the date for tool use and meat-eating in our lineage back by around 1 million years, our finds show that tool use and meat-eating was not unique to (the genus) Homo," co-author Zeresenay Alemseged told Discovery News.
"Also, by showing that A. afarensis was involved in these activities, we showed that you do not need a large brain to do this," added Alemseged, director of the Department of Anthropology at the California Academy of Sciences.
Brown agrees that braininess may not always explain how much or little certain species use tools.
"Are there physical and or ecological constraints on tool use?" he said. "Hopefully if we do this we can get away from the notion that 'humans use tools so tool-users must be smart like humans.' That idea seems to be leading us in circles."